The present invention relates to a motor controller and an electric power steering apparatus having the motor controller.
In many cases, a motor controller provided in an electric power steering apparatus (EPS) includes anomaly detecting means that detects an anomaly such as a failed electric current flow caused in any one of phases of a motor, that is, U, V, or W-phase, due to a break of a power supply cable or a failed contact of a driver circuit. Normally, if an anomaly is detected by the anomaly detecting means, the motor is quickly stopped to perform fail-safe. This greatly changes steering characteristics of the EPS, requiring the driver to increase the force applied to the steering wheel.
In this regard, for example, Japanese Laid-Open Patent Publication No. 2003-26020 discloses a motor controller that continuously operates a motor using two phases other than a phase with a failed electric current flow even after such failure has been detected in the phase. In this manner, assist force is continuously applied to a steering system so as to assist in manipulation of a steering wheel by the driver. This suppresses increase of load on the driver.
However, even if the motor is continuously actuated in the manner described above by two phases other than the phase in which a failure of electric current flow has occurred, in the case that the sinusoidal electric current is fed to each of these two phases (in the case that the sinusoidal electric current is fed to the V-phase and the W-phase while a failure of electric current flow has occurred in the U-phase, for example, as shown in FIG. 27), a torque ripple is caused and steering comfort is decreased due to the torque ripple. Specifically, with reference to FIG. 28 in which change of the motor electric current in the two phase drive mode is represented in a d/q coordinate system, the actual q-axis electric current value changes in a sinusoidal manner despite a constant q-axis electric current command value, which is a target control value of the motor torque. Thus, the motor is continuously operated without obtaining a motor electric current matching a required torque.
Further, in many cases, the detection of an anomaly in the control system such as the generation of an overcurrent caused by a failure of the drive circuit and a sensor anomaly is carried out on the basis of a comparison between an electric current deviation in the d/q coordinate system (mainly the q-axis electric current deviation), and a predetermined threshold value (for example, refer to Japanese Laid-Open Patent Publication No. 2006-67731). However, since each of the electric current values is changed in the sinusoidal shape in the d/q coordinate system at a time of the two-phase drive mode, as described above, the electric current deviation is generated regardless of whether there is an anomaly in the control system. Accordingly, there is a problem that an anomaly cannot be detected at a time of the two-phase drive mode.